Internal combustion engines may be operated to generate power. In order to maximize the power generated by the internal combustion engine, the engine may be equipped with a turbocharged induction system. A turbocharged induction system may include a turbocharger having a compressor that compresses the air flowing into the engine. The turbocharger typically also includes a turbine connected to the compressor and driven by an exhaust of the engine. Since the intake air is compressed by the compressor, more air per unit volume may be forced into a combustion chamber of a turbocharged engine than possible with a naturally-aspirated engine. As a result, more power can be generated by a turbocharged engine than a naturally-aspirated engine of the same size.
In engines such as natural gas engines, engine speed or load is controlled by adjusting the flow of a mixture of air and fuel into the combustion chambers of the engine. When an increase in speed or load is desired, the flow of the air/fuel mixture to the natural gas engine is increased using a throttle valve or other like flow control device. On the other hand, if a decrease in engine speed or load is desired, the flow of the air/fuel mixture to the engine is decreased.
While reducing the flow of the air/fuel mixture to the natural gas engine may be useful in reducing engine speed or load, such flow reductions can have adverse effects in certain operating conditions. For example, if a relatively rapid decrease in engine speed or load is required, flow of the air/fuel mixture into the engine may be slowed relatively abruptly by the flow control device. The decreasing mass flow rate through the compressor at a set compressor pressure ratio results in an oscillating flow reversal within the compressor known as “compressor surge.” Such compressor surge can be detrimental to component life and is not desirable.
In engines such as diesel engines, on the other hand, engine load or speed is controlled quite differently. Whereas the load or speed of a natural gas engine is controlled by manipulating the flow of the air/fuel mixture provided to the engine, the load or speed of a diesel engine is controlled by adjusting the amount of fuel that is injected into the respective combustion chambers of the engine. Since airflow is not manipulated in a diesel engine via, for example, an air flow control valve such as a throttle valve, the compressor is not subject to the decreasing mass flow at a given pressure ratio and, thus, the compressor is not forced into compressor surge. Thus, while compressor surge may have a profound impact on the functionality and efficiency of a natural gas engine, a diesel engine is not operated in a way that triggers compressor surge conditions.
One method of avoiding compressor surge in natural gas engines is to provide a bypass system, whereby excess compressed air/fuel mixture can be selectively released from downstream of the compressor. One such bypass system is shown in U.S. Patent Application Publication No. 2009/0139230 (“the '230 publication”). The system taught in the '230 publication includes a natural gas engine, and a turbocharger receiving a flow of exhaust from the engine. The exhaust is directed to a turbine of the turbocharger, and the turbine is connected to a compressor which assists in compressing a mixture of air and fuel upstream of an intake manifold of the engine. The system further includes a bypass line fluidly connected to an outlet of the compressor. The bypass line is configured to direct a portion of the compressed air/fuel mixture from the compressor outlet to an inlet of the compressor.
Although the system taught in the '230 publication may be useful in avoiding compressor surge, the disclosed system may result in energy loss in certain engine operating conditions. In particular, by directing a portion of the compressed air/fuel mixture back to a relatively low pressure area at the inlet of the compressor, the energy expended by the system to compress this portion of the mixture goes unused.
The power system of the present disclosure solves one or more of the problems set forth above.